1. Field of the Invention
The present invention relates to a micromechanical structure, e.g., an acceleration sensor having a seismic mass.
2. Description of the Related Art
Such structures are generally known. For example, an acceleration sensor is known from published German patent application document DE 197 19 779 A1, having a seismic mass which is movably suspended on a substrate via suspension springs. When the acceleration sensor accelerates, inertial forces act on the seismic mass which deflect the seismic mass relative to the substrate. The extent of this deflection is measured with the aid of detection means. The detection means include a comb electrode structure composed of fixed electrodes attached to the substrate and counter electrodes attached to the seismic mass. The deflection is measured by evaluating the change in electrical capacitance between the fixed electrodes and the counter electrodes. In these types of structures, the seismic mass, the suspension springs, and the counter electrodes are provided in a single functional layer made of polycrystalline silicon (referred to below as “first functional layer”), so that these structures are always situated next to one another. A printed conductor plane made of a thin polycrystalline layer, provided between the substrate and the seismic mass and separated from the substrate wafer by an insulating oxide, is used for the electrical contacting.
For producing micromechanical structures, it has also been proposed in published German patent application document DE 10 2007 060 878 A1 to use an additional functional layer made of polycrystalline silicon (referred to below as “second functional layer”). Published German patent application document DE 10 2009 000 167 A1 discloses, for example, an acceleration sensor which is constructed using two separate functional layers, while a yaw rate sensor is known from published German patent application document DE 10 2009 000 345 A1 which has Coriolis elements for measuring a rotational speed, and which is constructed using two separate functional layers. The yaw rate sensor has a first and a second Coriolis element which are connected to one another via a coupling spring, and which with the aid of drive means are excited to vibrate in phase opposition parallel to a first axis, a first and a second detection means detecting a deflection of the first and second Coriolis elements based on a Coriolis force which acts on the Coriolis elements when a yaw rate is present, so that the difference in a first detection signal of the first detection means and a second detection signal of the second detection means is a function of the Coriolis force, and thus, also a function of the rotational speed of the yaw rate sensor.